1. Field of the Invention
The present invention relates to a method of fabricating a gate cap layer, and more particularly to a method of fabricating a gate cap layer by using a sacrifice layer having a variable composition.
2. Description of the Prior Art
Metal gate electrodes have evolved for improving the drive current by reducing polysilicon depletion. Replacement gate techniques have been developed to substitute metal gate electrodes for polysilicon gate electrodes. For example, a polysilicon gate is used during initial processing until a high temperature annealing process to activate source/drain region. Subsequently, the polysilicon gate is removed and replaced with a metal gate.
As transistor pitch scales down, self-aligned (SAC) contacts are essentially required to avoid gate to source/drain contact shorts, to reduce source/drain resistance by enabling an increase in the width of contact plugs, and to increase the lithography/etching process window. Formation of a cap layer on top of the replacement metal gate structure is a key process to prevent contact shorts between the contact plugs and the metal gates. However, a serious problem associated with this cap layer technique is that after forming the cap layer, dishing phenomenon occurs on the cap layer.